This invention relates in general to the manufacture of structural members having desired shapes, such as components for use in vehicle frame assemblies. More specifically, this invention relates to an improved apparatus and method for initially performing a heat treatment process on a closed channel structural member to facilitate the performance of a subsequent deforming process so as to manufacture a vehicle frame component having a desired shape for use in such a vehicle frame assembly.
Many land vehicles in common use, such as automobiles, vans, and trucks, include a body and frame assembly that is supported upon a plurality of ground-engaging wheels by a resilient suspension system. The structures of known body and frame assemblies can be divided into two general categories, namely, separate and unitized. In a typical separate body and frame assembly, the structural components of the body portion and the frame portion are separate and independent from one another. When assembled, the frame portion of the assembly is resiliently supported upon the vehicle wheels by the suspension system and serves as a platform upon which the body portion of the assembly and other components of the vehicle can be mounted. Separate body and frame assemblies of this general type are found in most older vehicles, but remain in common use today for many relatively large or specialized use modern vehicles, such as large vans, sport utility vehicles, and trucks. In a typical unitized body and frame assembly, the structural components of the body portion and the frame portion are combined into an integral unit that is resiliently supported upon the vehicle wheels by the suspension system. Unitized body and frame assemblies of this general type are found in many relatively small modern vehicles, such as automobiles and minivans.
Traditionally, the various components of known vehicle body and frame assemblies have been formed from open channel structural members, i.e., structural members that have a non-continuous cross sectional shape (U-shaped or C-shaped channel members, for example). Thus, it is known to use one or more open channel structural members to form the side rails, the cross members, and other components of a vehicle body and frame assembly. However, the use of open channel structural members to form the various components of a vehicle body and frame assemblies has been found to be undesirable for several reasons. First, it is relatively time consuming and expensive to bend portions of such components to conform to a desired final shape, as is commonly necessary. Second, after such bending has been performed, a relatively large number of brackets or other mounting devices must usually be secured to some or all of such components to facilitate the attachment of the various parts of the vehicle to the body and frame assembly. Third, in some instances, it has been found difficult to maintain dimensional stability throughout the length of such components, particularly when two or more components are welded or otherwise secured together.
To address this, it has been proposed to form one or more of the various vehicle % body and frame components from closed channel structural members, i.e., structural members that have a continuous cross sectional shape (tubular or box-shaped channel members, for example). This cross sectional shape is advantageous because it provides strength and rigidity to the vehicle body and frame component. Also, this cross sectional shape is desirable because it provides vertically and horizontally oriented side surfaces that facilitate the attachment of brackets and mounts used to support the various parts of the vehicle to the body and frame assembly. In some instances, the various parts of the vehicle may be directly attached to the vertically and horizontally oriented side surfaces of the vehicle body and frame assembly.
In vehicle body and frame assemblies of the type described above, many of the various vehicle frame components do not extend linearly throughout their entire lengths. As a result, it is usually necessary to bend or otherwise deform portions of the vehicle frame components to achieve these relatively complex shapes. Unfortunately, it has been found to be relatively difficult to bend or otherwise deform closed channel structural members into desired configurations, particularly when the desired configuration contains one or more relatively sharp bends. In the past, a conventional mechanical bending machine, such as a tube bender, has been used to apply sufficient forces to the closed channel structural member as to deform it to a desired angle. However, the amount by which a closed channel structural member may be deformed by a conventional tube bender or similar mechanical bending machine is limited. Excessive bending can result in fracturing or other damage to the closed channel structural member. This is particularly true when the size of the closed channel structural member is relatively large, as is typically found in vehicle frame components. When attempting to form a relatively sharp bend in a relatively large closed channel structural member, excessive compression occurs at the inner bending radius, while excessive stretching occurs at the outer bending radius of the tube. This generally results in undesirable buckling of the closed channel structural member at the inner bending surface and undesirable stretching or fracturing of the closed channel structural member at the outer bending radius.
To address this, it is known that a closed channel structural member can be heat treated prior to the performance of a bending process so as to increase the ductility thereof. Such a heat treatment process can be performed on the closed channel structural member either in whole or in part and can, for example, consist of a retrogression heat treatment process. A retrogression heat treatment process is performed by rapidly heating a closed channel structural member to a sufficient temperature that provides for full or partial softening thereof, followed by relatively rapid cooling. Notwithstanding this cooling, the closed channel structural member retains the full or partial softening characteristics for at least a relatively short period of time. It is during this relatively short period of time that the deforming process can be performed with relative ease. Thereafter, however, as more time passes, the closed channel structural member re-hardens, and such bending becomes more difficult.
It is well known that vehicle frame components are usually manufactured in relatively large quantities. Therefore, to insure optimum efficiency in the manufacturing operation, any process to be performed on a vehicle frame component must be capable of being performed in a relatively quick and efficient manner. Although it is known to perform a retrogression heat treatment process on a vehicle frame component prior to bending the component, as discussed above, such known methods have been found to be undesirably slow in the context of the manufacture of vehicle frame components. Thus, it would be desirable to provide an improved apparatus method for manufacturing a vehicle frame component that allows a preliminary heat treatment process to be performed in a relatively quick and easy manner so as to facilitate the subsequent performance of a bending or other deforming process.